Leaders are tested—especially their abilities and their commitment—in times of turmoil and uncertainty. That’s when leaders replace imposters, when champions take over from those who merely occupy a corner office. True leaders often appear in times of stress—be it financial, emotional, political or physical. As a student and as a teacher of leadership, I’ve long been impressed with how military officers in particular lead precisely when it’s not convenient or easy—when the tumult is the greatest and uncertainty is at a peak.

We’ve come to expect such leadership from them. When a bomb went off at the finish line of the Boston Marathon in 2013, U.S. Army Colonel Everett Spain—at the time, a Harvard Business School student—ran toward the explosion, into the smoke, to help victims. “I can say with perfect honesty that it was not me who ran toward the smoke,” he later explained, “but the values deliberately imprinted on me by my faith, my family, my friends, my mentors, the many character-building institutions I’ve been privileged to be associated with, and our American spirit.”

This past summer, Alek Skarlotos—a specialist in the Oregon National Guard—and Spencer Stone—an airman in the U.S. Air Force—were on vacation, aboard a high-speed train bound for Paris. Suddenly, they heard gunshots and breaking glass. Rather than head for cover, they ran toward the chaos, to subdue a terrorist armed with an AK-47.

And there’s Jake Harriman, who served more than seven years in the U.S. Marine Corps as a platoon commander in both the infantry and a Special Ops unit called Force Recon. His service included two combat tours in Iraq. On his return to this country, Jake came to Stanford to earn his MBA – but instead of accepting lucrative work on Wall Street or in consulting after graduation he headed back into the fray—this time to fight poverty in strife-torn regions, to “serve the poorest of the poor,” as he put it.

When I talk to such service members and those who know them, I try to discover what it is that makes them special—why others want to follow them. What I’ve learned can be summarized by five attributes (illustrated with some of my favorite quotes):

Leaders don’t need to be asked. (The motto of the U.S. Army Rangers isSua Sponte—“of their own accord”—meaning they chose their duty.)

Leaders do themselves what they ask of others. (“You can preach a better sermon with your life than with your lips.” –Oliver Goldsmith)

Leaders are prepared. (Navy SEALs “earn their Trident every day,” according to their code.)

Leaders are all about the mission. (“Never mind your happiness; do your duty.” – Peter Drucker)

We live in a time when leadership is hotly debated – in national politics, in the boardroom, in the academy. Some believe leadership is a product of title. Others suggest it’s a function of power. But the performance of real leaders like Spain, Skarlotos, Stone and Harriman demonstrate that it’s not about station or might. Those among us who aspire to leadership can learn important lessons from these service members who, in running toward the fire, show us what Dr. King meant by leadership in times of challenge.